1. Field of the Invention
The present invention relates to a radio frequency (RF) probe for measuring the RF characteristics of a semiconductor device on a wafer, and a probe card including the radio frequency probe.
2. Description of the Related Art
In general, the RF characteristics of a semiconductor device is measured after the semiconductor device is assembled in a package of ceramic and the like. This is because, by providing lead terminals to the package, a packaged semiconductor device can be electrically connected to an outer circuit under predetermined conditions with good reproducibility, and thus the RF characteristics of the semiconductor device can be stably measured.
In recent years, for the realization of smaller-size apparatuses, chips of RF semiconductor devices are increasingly mounted directly onto a circuit board and the like without being packaged. The measurement of the RF characteristics of such semiconductor devices is therefore carried out in the form of chips. This measurement is made, for example, by a known method using a radio frequency probe, where a ceramic substrate on which a coplanar type RF transmission line is formed is brought into direct contact with a wafer, so as to measure S parameter of a semiconductor device. A radio frequency probe for digital signals is also known.
However, the coplanar type radio frequency probe is not only expensive, but also inferior in operational life as the top end of the probe wears by contact with the wafers. The coplanar type radio frequency probe is also disadvantageous in that an impedance matching circuit cannot be formed therein. Due to the failure in impedance matching between the measuring apparatus and the semiconductor device, an RF power input into the semiconductor device is largely reflected by the semiconductor device. As a result, correct measurement is not possible.
The radio frequency probe for digital signals can transmit a digital signal of several tens of MHz. However, since a grounding electrode of the radio frequency probe is not in direct contact with a chip, the grounding potential of the chip is different from that of the radio frequency probe. This prevents the transmission of RF power, especially the transmission of an RF power exceeding 1 GHz because of the large variation in impedance.
For the above reasons, a radio frequency probe has not been developed which can measure the analog RF characteristics of a semiconductor device on a wafer.
Conventionally, when a semiconductor device is packaged and used as an electronic component, the semiconductor device is tested according to a procedure as shown in FIG. 8. First, semiconductor devices formed on a substrate is subjected to a DC test (step 101). Only the semiconductor devices having passed the DC test are cut into chips, which are then assembled in a package made of ceramic and the like (step 102). The packaged semiconductor devices are then subjected to an RF test (step 103). Packages containing the semiconductor devices having passed the RF test are finally mounted on a circuit board as components (step 104). According to the above procedure, whether or not a semiconductor device is defective is not determined until the semiconductor device has been packaged. This causes an increase in the production cost.
Assume that one wafer includes 1,000 semiconductor devices and that the yields at the DC test and the RF test are both 80%. Then, 160 of the packaged semiconductor devices are thrown away and not used as products due to poor RF characteristics. This means that 160 ceramic packages as well as the time required to package 160 inferior semiconductor devices have been wasted.